Aqueous alkaline manganese dioxide zinc batteries consume zinc metal particles during electrochemical discharge. Zinc particle electrodes have the advantage of high active surface area per gram of zinc which allows high average current densities without excessive polarization. The particles are made to contact a current collector. An aqueous electrolyte solution provides ionic conduction between the anode and the cathode. The aqueous electrolyte may also function as a reactant or provide reactants. The electrolyte solution is typically an aqueous alkaline electrolyte containing potassium hydroxide, sodium hydroxide, or a mixture thereof.
On discharge, the zinc particles produce electricity and a reaction product consisting of zinc hydroxides, zincate ions, or zinc oxides. Generally, conventional zinc particles have had irregular shapes. The elimination of mercury in the zinc anode of an electrochemical cell has resulted in poor electrical contact between the zinc particles and has led to an increase in corrosion. One method used to overcome poor electrical contact has been to use higher concentration of zinc in the anode. However, this reduces the space available for reaction products. Another method used to overcome poor electrical contact has involved concentrating the zinc by creating connected agglomerates of zinc. Patents and applications that describe the use of agglomerates include European Patent Application EP 414,990 A1; U.S. Pat. No. 4,963,447 to Nishimura et. al.; and U.S. Pat. No. 3,884,722 to Tucholski. Unfortunately, using the gelling agents described in these patents can impair the cell's discharge characteristics by inhibiting the reaction efficiency of the zinc.
Others in attempts to reduce anode gassing have compressed the zinc particles such as in Vu et al.; U.S. Pat. No. 4,743,185. Others have used zinc powders of a generally spherical shape such as in Japanese unexamined patent publication 4-296451. However, this publication teaches zinc apparent densities greater that 3.5 g/cc with anode zinc concentrations as high as 75 weight percent.
In order to achieve the highest electrochemical activity from the zinc particles with the highest particle-to-particle contact and electroconductivity, it is desirable to have an anode comprising zinc particles having uniform morphology and/or size. It would also be desirable to have zinc particles having the same porosity, chemical composition, reactivity, morphological, topological, and physical properties. Battery systems in which zinc particles of this invention may be used include alkaline manganese dioxide-zinc cells, zinc-air button cells, and the like, including primary and secondary batteries.